The present invention relates to a brushless motors used to drive a data storage device, and more particularly, to a thin type brushless motor used to drive a data storage device such as a floppy disk and a magneto-optic disk.
Generally, a brushless motor used to drive a data storage device such as a floppy disk and a magneto-optic disk is provided with a base plate to be mounted on a drive unit, a rotor rotatable relative to the base plate and a pair of bearings interposed between the base plate and the rotor. An annular rotor magnet is fixedly secured on the inner surface of the rotor and a stator is attached on the base plate so as to oppose the rotor magnet. Furthermore, the brushless motor is provided with a turntable which rotates with the rotor. The turntable has a table body and a chucking magnet secured on the table body. The data storage device is detachably mounted on the turntable by the magnetic action of the chucking magnet.
In recent years, a drive unit for use to rotate a data storage device such as a floppy disk and a magneto-optic disk are required to be small in axial height due to ongoing tendency of smaller and thinner designs of a notebook type personal computer and other similar equipment in which such a drive unit is mounted.
However, in the conventional brushless motor as mentioned above, a pair of bearings are arranged so as to be axially aligned and spaced apart from each other for stably supporting the rotor. In addition, the turntable is formed separately from the rotor and disposed on the top of the rotor. Therefore, the conventional brushless motor has limitation with respect to reduction of the axial height of the motor. If the motor is arranged to support the rotor by a single bearing for reducing the axial height of the motor, the rotational accuracy of the motor is deteriorated by the inclination of the shaft relative to the rotor and the run out of the rotor.
Furthermore, if the axial height of the motor is reduced, the axial clearance between the rotor and the base plate becomes small, thus, the amount of the coil to be wound around a stator core is limited and then sufficient driving force cannot be obtained.